The invention is in the field of Semiconductor-On-Insulator (SOI) devices, and relates more particularly to Lateral Insulated Gate Bipolar Transition (LIGBT) SOI devices suitable for high-voltage applications.
In fabricating high-voltage power devices, tradeoffs and compromises must typically be made in areas such as breakdown voltage, size, "on" resistance, saturation current and manufacturing simplicity and reliability. Frequently, improving one parameter, such as breakdown voltage, will result in the degradation of another parameter, such as "on" resistance. Ideally, such devices would feature superior characteristics in all areas, with a minimum of operational and fabrication drawbacks. One particularly advantageous form of lateral thin-film SOI device includes a semiconductor substrate, a buried insulating layer on the substrate, and a lateral transistor device in an SOI layer on the buried insulating layer, the device, such as a MOSFET, including a semiconductor surface layer on the buried insulating layer and having a source region of a first conductivity type formed in a body region of a second conductivity type opposite to that of the first, an insulated gate electrode over a channel region of the body region and insulated therefrom by a surface insulation region, a lightly-doped lateral region such as a linearly-graded lateral drift region of the first conductivity type, and a drain region of the first conductivity type laterally spaced apart from the channel region by the drift region.
However, SOI MOSFET devices such as those described above still suffer from certain drawbacks, such as requiring a relatively large area for a given current carrying capacity and high "on" resistance in smaller-area devices. In order to overcome these disadvantages, various types of Lateral Insulated-Gate Bipolar Transistor (LIGBT) designs have been developed, as illustrated in U.S. Pat. Nos. 4,963,951, 5,654,561 and 5,869,850. Although these prior-art LIGBT designs generally offer the advantages of improved current capacity and have various features to improve immunity to latch-up, further improvement in on-state performance (saturation current) would be desirable in order to further increase current capacity and/or reduce device area for a given saturation current value.
Thus, it will be apparent that numerous techniques and approaches have been used in order to enhance the performance of power semiconductor devices, in an ongoing effort to attain a more nearly optimum combination of such parameters as breakdown voltage, size, saturation current and manufacturing ease. While the foregoing structures provide varying levels of improvement in device performance, no one device or structure fully optimizes all of the design requirements for high-voltage, high-current operation.
Accordingly, it would be desirable to have an LIGBT SOI device structure capable of high performance in a high-voltage, high-current environment, in which operating and fabrication parameters, and in particular on-state performance (saturation current) and/or reduced area are further optimized.